Short answer: Yes. Taking more antihistamine than the label directs can cause an overdose. Most people recover with prompt medical care, but first-generation antihistamines like diphenhydramine (Benadryl) can cause serious symptoms at high doses, especially when combined with opioids, sedatives or alcohol. If you suspect an overdose, call Poison Control at 1-800-222-1222, or 911 if the person is unconscious or delirious.
An estimated 40 to 50 million people in the United States live with allergies, and antihistamine pills are among the most common treatments. While these drugs can reduce sneezing, itchy eyes, congestion and other symptoms, they can also cause side effects — particularly for those who take too much allergy medication. Let’s look at the risk factors and symptoms of an antihistamine overdose, and how to use these medicines safely.
Understanding Antihistamines
Allergies occur when the immune system identifies a harmless substance, such as pet dander or grass pollen, as a threat. The immune system releases chemicals that trigger an inflammatory response to protect the body.
Histamine is one of the key immune system chemicals involved in allergic reactions. Antihistamine medications work by interfering with the effects of histamine. While prescription versions of these drugs are available, most people take over-the-counter allergy medicines.
Two main types of OTC allergy medications exist: first-generation and second-generation.
- First-generation antihistamines include diphenhydramine (Benadryl), brompheniramine, dimenhydrinate (Dramamine) and doxylamine. These medications also act on the part of the brain responsible for controlling nausea, so they’re used to treat motion sickness in addition to allergies.
- Second-generation antihistamines include loratadine (Claritin), cetirizine (Zyrtec) and fexofenadine (Allegra). These medications affect different areas of the brain and spinal cord to provide longer-lasting relief from allergy symptoms.
Among prescription antihistamine medications, hydroxyzine is a unique option. In addition to blocking the effects of histamine, this drug interferes with the activities of the brain chemical acetylcholine, which controls arousal and involuntary muscle movements. Due to its actions, hydroxyzine has a calming effect on the body and mind and is sometimes prescribed for anxiety.
Can You Overdose on Benadryl or Other Allergy Medication?
Antihistamine overdoses can occur when you take too much of an anti-allergy medication. While many people associate overdoses with severe medical outcomes or even death, overdosing on allergy medication means exceeding the recommended dosage and experiencing adverse effects.
Some antihistamine overdoses are unintentional. When symptoms aren’t well controlled, people may take more than the label directs in search of relief, which raises the risk of an overdose without their realizing it.
Others deliberately misuse certain antihistamines for their psychoactive effects. Taking too much diphenhydramine can cause euphoria, and the CDC notes that antihistamine misuse has been documented primarily among adolescents and young adults.
First-generation antihistamines, also known as sedating antihistamines, are more likely to cause serious overdose symptoms than other anti-allergy medications. Benadryl, Dramamine and other first-generation medications can cause drowsiness and may interact with other medications, increasing the risk of serious side effects when taken excessively.
Second-generation antihistamines, or nonsedating antihistamines, are considered safer options because they don’t cross the blood-brain barrier the way first-generation medications do. They’re less likely to cause severe or life-threatening side effects, but you can still overdose on Allegra and other second-generation antihistamines if you exceed the recommended dose.
The effects of an antihistamine overdose can occur within an hour or two of ingesting the medication. Symptoms vary depending on how much was taken, the person’s age and their overall health. Signs may include an abnormally fast or irregular heartbeat, visual disturbance, and high or low blood pressure. First-generation overdoses are more likely to cause neurological symptoms such as hallucinations and drowsiness.
Most people recover from antihistamine overdoses with the right medical support. In some cases, though, overdosing on allergy medication can lead to multiorgan failure, so seeking rapid assistance matters. If you’re struggling to control your allergy symptoms, ask your doctor for advice rather than increasing your dosage or mixing antihistamines. Your provider can evaluate your situation and recommend a safe, effective treatment plan.
Dosing Recommendations: How Much Is Too Much Allergy Medication?
Over-the-counter and prescription antihistamines carry clear dosing instructions. For most first-generation OTC medications, the label advises taking the medication every four to six hours. Second-generation OTC antihistamines typically direct one pill every 12 or 24 hours.
These are general guidelines. How much medication is safe for a given person depends on age, tablet strength and the condition being treated, so your doctor or pharmacist may recommend a different regimen.
Whether you’re taking antihistamines for allergies, anxiety or motion sickness, following the dosage instructions is the single most effective way to prevent an overdose. Read the packaging carefully, and take only the number of pills suggested as often as recommended unless a health care provider advises otherwise.
Potential Benadryl Overdose Symptoms
Because antihistamines are available over the counter, it’s easy to assume these medications carry no real side effects or overdose risk. That isn’t the case.
Side Effects of First-Generation Antihistamines
Common side effects of first-generation antihistamines include:
- Blurred vision
- Constipation
- Dizziness
- Double vision
- Drowsiness
- Dry mouth
- Headaches
- Low blood pressure
- Rapid heart rate
- Thickening of mucus in the airways
- Trouble urinating
First-generation antihistamines have anticholinergic properties, which may increase the risk of dementia and other side effects in older adults. Consulting a doctor before taking first-generation antihistamines is wise if you’re 65 or older.
Because first-generation antihistamines often cause drowsiness, people sometimes take them as sleep aids. Over time, the body can build tolerance, and it takes more of the drug to produce the same drowsiness. Taking more than recommended to induce sleep is a common route to an accidental overdose.
Some people also take too much allergy medication intentionally, to experience a high. At high doses, diphenhydramine can cause delirium, seizures, psychosis and death.
Side Effects of Second-Generation Antihistamines
Potential side effects of second-generation antihistamines include:
- Abdominal pain
- Cough
- Fatigue
- Headache
- Nausea
- Sore throat
- Vomiting
People are less likely to misuse second-generation antihistamines because these medications don’t produce the drowsiness first-generation allergy medications can. Most often, overdoses are accidental and occur when someone forgets they already took their daily dose. A single extra dose increases the risk of side effects but is unlikely to prove fatal.
As a result, Allegra, Zyrtec and Claritin overdose deaths are rare. Any overdose can still be dangerous, so avoid taking more than the recommended dose.
Risk Factors for Antihistamine Overdose
Some people are at increased risk for antihistamine overdose because of other medications they take or medical conditions they have.
Other drugs that cause drowsiness can intensify the sedative effect of first-generation antihistamines. Experts generally recommend not taking these drugs alongside other sleep aids, muscle relaxants, sedatives, seizure medications and some antidepressants.
Diphenhydramine and opioid pain relievers are an especially dangerous combination. Analyzing overdose deaths across 44 jurisdictions during 2019 and 2020, the CDC found that antihistamines were detected in 14.7% of overdose deaths and were listed as a cause of death in 3.6%. Fewer than 0.1% involved antihistamines alone — the large majority also involved opioids, primarily illicitly manufactured fentanyl. The CDC also notes that antihistamines don’t respond to naloxone, so an overdose involving both opioids and antihistamines may require naloxone plus additional emergency medical care.
Hydroxyzine can interact with all the drugs mentioned above, as well as other medications that suppress the activities of acetylcholine. Your doctor may recommend a different antihistamine if you take tricyclic antidepressants, certain antipsychotics or some anti-nausea drugs.
Certain medical conditions can also heighten the risk of side effects of antihistamines and the risk of overdose. Generally, people with glaucoma, thyroid issues and heart disease should avoid first-generation antihistamines, and individuals with kidney or liver disease may not be good candidates for second-generation antihistamines.
Regardless of your health history, it’s worth consulting your medical provider before taking any OTC antihistamine for the first time. They can guide you on proper dosage and potential side effects.
What to Do in a Suspected Overdose
If you or someone you know has taken too much allergy medication, seek medical help right away. Prompt treatment substantially reduces the risk of serious harm from an overdose of Zyrtec, Benadryl or another antihistamine.
If the person is awake and responsive, contact Poison Control at 1-800-222-1222 for guidance on next steps. If someone is unconscious, having a seizure or delirious, call 911.
Why People Misuse Antihistamines
Antihistamines sit alongside cough medicines and decongestants among the over-the-counter drugs most often misused. For many people, misuse doesn’t start as misuse at all — it starts with taking an extra pill for the sedating or drowsy feeling while managing a cold or allergies. Over time, tolerance builds, and it takes higher doses to produce the same effect. That pattern is how dependence on an ordinary drugstore medication can develop without anyone naming it.
Frequently Asked Questions
Can you die from an antihistamine overdose?
It’s possible but uncommon. Deaths from second-generation antihistamines such as Claritin, Zyrtec and Allegra are rare. First-generation drugs like Benadryl carry more risk, particularly when combined with opioids, sedatives or alcohol. CDC data from 2019 to 2020 found antihistamines listed as a cause of death in about 4% of overdose deaths, and fewer than 0.1% of those deaths involved antihistamines alone.
What are the signs of an antihistamine overdose?
Signs can include an abnormally fast or irregular heartbeat, blurred or double vision, high or low blood pressure, confusion, extreme drowsiness and hallucinations. Symptoms vary with the amount taken, the person’s age and their overall health, and neurological symptoms are more common with first-generation antihistamines.
How quickly do antihistamine overdose symptoms appear?
Symptoms typically begin within one to two hours of taking the medication. If you suspect an overdose, don’t wait for symptoms to develop before calling Poison Control at 1-800-222-1222.
Is it safe to take antihistamines as a sleep aid?
Occasional short-term use is common, but first-generation antihistamines aren’t intended for ongoing sleep support. The body builds tolerance to their sedating effect, which can lead people to take more than the label directs. If you’re relying on antihistamines to sleep regularly, talk with your doctor about the underlying sleep problem instead of increasing the dose.
Can you become dependent on antihistamines?
Psychological dependence can develop, particularly with first-generation antihistamines used for their sedating or euphoric effects. As tolerance builds, higher doses are needed for the same effect, which raises overdose risk. If stopping feels difficult or you find yourself taking more than intended, that’s worth discussing with a professional.
Get Support for Allergy Medication Misuse
If you’re concerned about taking too much allergy medication, or you’re using antihistamines to manage anxiety or sleep and it’s gotten harder to stop, help is available. Sunlight Recovery provides addiction treatment in South Florida with the clinical capacity to address co-occurring mental health conditions through dual-diagnosis care. Our admissions line is answered 24/7 at (855) 625-6684, or you can get in touch here. Every conversation is confidential, with no obligation.
If you or someone you know is in emotional distress or thinking about self-harm, call or text 988 to reach the Suicide & Crisis Lifeline, available 24 hours a day.
